1. Bieri, R., Geoghegan, R.: Sigma invariants of direct product of groups, preprint (2008)
2. Bieri, R., Geoghegan, R., Kochloukova, D.: The sigma invariants of Thompson’s group F, preprint (2008)
3. Bieri R., Neumann W., Strebel R.: A geometric invariant of discrete groups. Invent. Math. 90(3), 451–477 (1987)
4. Bieri R., Renz B.: Valuations on free resolutions and higher geometric invariants of groups. Comment. Math. Helv. 63(3), 464–497 (1988)
5. Bieri, R., Strebel, R.: Geometric invariants for discrete groups (monograph in preparation)